The invention concerns a system for the securing of objects located in a room presenting at least one room outlet, in particular a (self-service) place of sale (such as for example a supermarket), against theft and burglary. The objects to be secured are each equipped with at least one magnetically activatable sensor metal element. A first apparatus is arranged at each room outlet to generate a magnetic field, in the area of which field the magnetically activated sensor metal element, arranged on an object to be secured, generates a detectable signal when a field strength limit value is exceeded. A second apparatus associated with the first apparatus detects the generated signal, which in the event of its occurrence is conducted to an alarm apparatus, so as to trigger an alarm.
The invention furthermore concerns a sensor metal element suitable for this purpose, as well as the use of a section of a Wiegand wire as a sensor metal element for a magnetic security system of the kind under discussion here.
When reference is made above or below to a "room outlet," this does not necessarily need--particularly in the case of the use of a system according to the present invention as a merchandise theft security system in a place of sale or exhibition--to involve an exit from the room in question, which leads either outdoors or into another room and accordingly is let into a bordering wall of the room in question. Instead, it may also involve a passage or the like arranged within the room in question (for example, at a cash register), bounded in a suitable manner, as is referred to in general in the pertinent technical field generally as a control gate, i.e., a passage through which persons must pass in order to leave the room, particularly a delimited part of the room, if they want to leave the part of the room in question. On the other hand, in the case of the use of the system under the invention as a burglary security system, as a general rule a conventional entrance/exit will be involved, as additionally will be windows, floor or cellar hatches, and the like, i.e., room outlets that are present in a wall, the ceiling or the floor of the room to be secured. Security against theft of merchandise kept ready for sale in places of sale is called for not only for relatively high-value merchandise, but also for lower-value objects, since regrettably such crimes against property are not limited to higher-value goods. Rather, on the basis of corresponding investigations, one proceeds on the assumption that for example in so-called supermarkets or similar places of sale, in which the merchandise kept in stock is picked up in each case by customers as needed (generally in a shopping basket or cart) and is then paid for at a cash register, the loss of merchandise resulting from theft refers practically to all offered merchandise, and amounts in sum to more than 1% of the total turnover. This value is consequently extremely high, particularly in view of the relatively low profit margins of such places of sale, and requires corresponding countermeasures.
In addition to various other attempts to effectively secure merchandise against theft, various magnetic systems are known. These systems are still unsatisfactory, both in the technical regard (including their effectiveness) and in the economic regard. Such known magnetic theft security systems are frequently suitable from the outset for only a limited use, if only because of the investments to be performed with respect to the necessary apparatus, on the one hand, and the sensor elements to be used, on the other hand. For if, for example, the average profit margin of a supermarket is 1% of the merchandise value and the value of a given item of merchandise amounts to 5.00 DM, then it is obviously not economically sound to secure such an object with a (non-reusable) sensor metal element that costs 6 pfennigs, thus eliminating the profit to be earned. Moreover, the above example is by no means unrealistic; it is actually a conservative estimate of the cost of such sensor elements. Other sensor metal elements for use with magnetic theft security systems cost even more (for example approx. 0.25 DM), and accordingly, if only for economic reasons, can at best be used for very high-value merchandise with a corresponding merchandise value.
The known theft security systems on a magnetic basis, however, furthermore also present considerable technical defects, as will be explained in detail further below. A particularly grave defect, among others, is that false alarms occur relatively frequently. False alarms not only delay the planned brisk execution of sales (and in this way lead to a corresponding annoyance of customers), but also very frequently have the effect of annoying customers who on the basis of a false alarm have been exposed as a presumed thief and who must undergo a corresponding investigative procedure. Many such customers in the future avoid a place of sale equipped with such a theft security system, because the risk of a false alarm is too great for them and the circumstances associated with an--albeit unfounded--suspicion are unpleasant, so that in this way over the course of time a place of sale loses a not inconsiderable turnover.
In known theft security systems of the class under discussion here, the sensor metal elements to be fastened in each case to an object to be secured consist in each case of a metal strip, which consists of a highly permeable metal, preferably a corresponding metal alloy with a markedly rectangular hysteresis loop. In addition, the metal strips forming the sensor elements must be fastened with a separate security label to an object to be secured, because the price tags commonly used for labeling are too small to be able to be equipped with such a metal strip. A length of, for example, 7 cm is necessary for the sensor metal elements of current systems, in order to be able to generate the desired signals. In this connection, it should be noted that because of the necessary size of the sensor, which thereby necessitates separate labeling, security costs in the case of such a system are still further increased due to the additional work step required to equip an object with such a sensor element.
A further drawback of such or similarly configured sensor elements is that because of their size they are relatively readily recognizable by potential thieves, and accordingly can be easily discovered and if applicable rendered ineffectual by tearing off or the like. In the case of certain sensor elements for known electromagnetic theft security systems, in which the sensor elements are configured in the form of a printed circuit that is applied on a corresponding security label, not even a removal of the sensor element is needed in order to render this element ineffectual. Rather, for this purpose it is sufficient merely if individual conductor segments are cut by means of a sharp object, for which purpose for example even a fingernail may suffice.
In a typical theft security system, if an object equipped with a magnetically activated sensor metal element is brought to a room outlet in a supermarket or the like, i.e., for example to a control gate set up adjacent to a cash register, at which gate an (alternating) magnetic field is generated by means of a corresponding apparatus, then harmonics are induced because of the non-linear hysteresis loop of the material of the sensor metal element in a corresponding apparatus, which essentially consists of an induction coil. These harmonics may be evaluated by means of a suitable electronic filter apparatus, so that when corresponding harmonics occur an acoustic and/or optical alarm is triggered (if applicable, the room outlet may be closed), thus indicating that a correspondingly secured object is being unauthorizedly removed from the room in question.
If, on the other hand, a correspondingly secured object is properly paid for and only afterward taken through a correspondingly equipped room outlet, its magnetization is deactivated after payment in such a way that during passage through the room outlet no harmonics occur that supply a signal for an unauthorized removal of a secured object.
Concretely, the apparatus of a known theft security system of such a type consequently consists, in addition to the already repeatedly mentioned strip-like sensor metal elements, the induction coil forming the pickup coil and the filter electronics, of an exciter coil, which generates the alternating electromagnetic field. This field drives the security strip, consisting of a low-retentivity metal, into saturation and then generates magnetic reversal processes in it because of the alternating field, which processes are detected with the induction coil. Then by means of the filter electronics the fundamental frequency is expediently suppressed and only the harmonics (generally lying between the second and twentieth harmonics, frequently reaching up into the 100-kHz range) are evaluated. Thus, it is important that these harmonics should be excited even at relatively low exciting field strengths, with which the previously known systems operate, but that nevertheless these harmonics to be generated and evaluated should differ as much as possible from signals generated by other objects besides sensor metal elements, such as by objects which a customer may be carrying with him or else has properly declared and paid for as merchandise for purchase. To achieve in the essentials these requirements, which in any case are not one hundred percent satisfiable, the magnet material of such a security strip serving as a sensor metal element must be both extremely highly permeable and also markedly rectangular with regard to its hysteresis loop. These requirements are satisfied well by certain high-Co, low-retentivity, amorphous alloys, which are nearly magnetostriction-free. In this connection a combination of a magnetically active strip with a magnetically half-hard material makes it possible to put out of operation the security function of a sensor metal element in the event of the authorized removal of a correspondingly secured article. For this purpose, for example, the half-hard part of the metal loop is magnetically reversed in a purposeful manner by an external field, and in this way linearizes the characteristic of the magnetically active strip part, by which means the harmonics supplying the signal that is desired in the event of an unauthorized removal are reduced so severely in amplitude that they are no longer detected as harmonics by the filter electronics and no longer trigger any alarm signal. Unfortunately in this regard also, matters do not remain as correspondingly wished, and despite a corresponding magnetic reversal, through misinterpretation of the signal, a false alarm occurs.